add method total_listeners() when feature std

src/lib.rs

@@ -479,6 +479,40 @@ impl<T> Event<T> {
 
         inner
     }
+
+    /// Return the listener count
+    ///
+    /// This is only available when `std` feature is enabled.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use event_listener::Event;
+    ///
+    /// let event = Event::new();
+    ///
+    /// assert_eq!(event.total_listeners().unwrap(), 0);
+    ///
+    /// let listener1 = event.listen();
+    /// assert_eq!(event.total_listeners().unwrap(), 1);    
+    ///
+    /// let listener2 = event.listen();
+    /// assert_eq!(event.total_listeners().unwrap(), 2);        
+    ///
+    /// drop(listener1);
+    /// drop(listener2);
+    /// assert_eq!(event.total_listeners().unwrap(), 0);        
+    ///
+    /// ```
+    #[cfg(feature = "std")]
+    #[inline]
+    pub fn total_listeners(&self) -> Result<usize, String> {
+        if let Some(inner) = self.try_inner() {
+            inner.list.total_listeners_wait()
+        } else {
+            Ok(0)
+        }
+    }
 }
 
 impl Event<()> {

src/std.rs

@@ -54,6 +54,14 @@ impl<T> List<T> {
             Err(_) => Err("<locked>"),
         }
     }
+
+    // Get the listener count by blocking
+    pub(crate) fn total_listeners_wait(&self) -> Result<usize, String> {
+        match self.0.lock() {
+            Ok(mutex) => Ok(mutex.len),
+            Err(_) => Err("MutexPoisoned".into()),
+        }
+    }
 }
 
 impl<T> crate::Inner<T> {